The present invention relates to a pneumatically-powered demand pump utilized in a post-mix beverage syrup dispensing system and, more specifically, to a control device which will stop the rapid cycling of the pump when there is no longer a supply of syrup at the pump inlet and will suppress surges in the syrup output from the pump.
Diaphragm pumps are widely used, particularly for pumping liquid solutions and highly viscous materials under conditions such that the viscosity of the fluid being pumped, the head on the suction side of the pump and the back pressure on the pump discharge may all vary depending on the use of the pump. Examples of such pumps are disclosed in U.S. Pat. Nos. 3,741,689 to Rupp; 4,123,204 to Scholle; and 3,172,698 to Hinz, et al. These pneumatically-powered demand pumps normally continue to pump until a predetermined outlet pressure is reached. The pump will continue to pump a particular fluid, such as syrup, until the inlet gas pressure to the pump from the pneumatic power supply can no longer overcome the fluid pressure in the outlet line of the pump. When the suction line of a demand pump is connected to an empty, nonvented container, the pump is unable to suck enough fluid so as to pressurize the outlet line to a level above the aforementioned inlet gas pressure, so the pump cannot turn itself off. Thus, the pump will dry cycle indefinitely under these circumstances, wasting gas and possibly damaging the pump. This condition can develop due to a blocked or defective suction line or an empty syrup supply package.
On occasions during the operation of a pneumatically-powered demand pump, a partially blocked or defective suction line may produce surging of the liquid being pumped. Such a condition leads to uneven supply of the liquid medium and poor quality control of the product produced. Although certain devices have been proposed which control and regulate the air input to such a pneumatically-powered system, in most instances these devices are electrically powered or vacuum operated. In the case of an electrically powered control device, the requirement for the use of electricity inherently is a negative feature, increasing the cost of the operation. The use of a vacuum sensing device at the pump inlet will only work with sealed, nonvented containers and will not work with vented containers. Vacuum sensing control devices also do not work well when used in conjunction with other vacuum-operated devices such as vacuum-operated switchover valves which are frequently used in syrup dispensing systems.